Combined magnetic transducer head and coupling transformer



Nov. 9, 1954 D. E. WIEGAND 2,594,109

COMBINED MAGNETIC TRANSDUCER HEAD AND COUPLING TRANSFORMER OriginalFiled Dec. 4, 1947 Da 1nd 5. m egalza IL: 7 M 7"" United States PatentCOWINED MAGNETIC TRANSDUCER HEAD AND CDUPLING TRANSFORMER David E.Wiegand, Villa Park, Ill., assignor to Armour Research Foundation ofIllinois Institute of Technology, Chicago, 1th, a corporation ofIllinois @riginal application December 24, 1947, Serial No. 793,727, newPatent No. 2,535,065, dated February 12, 1952. Divided and thisapplication August 18, 1951, Serial No. 242,57ti

This invention relates to a combined magnetic transducer head andcoupling transformer, and more particularly, to What is generally knownas a single-turn head with the turn going through the gap of the head.

Great improvements have been made in the magnetic recording field inrecent years, and to some extent this has been brought about by thedevelopment of relatively high coercive force materials which could beformed into a wire or tape for use as a magnetic record member. It hasbeen found that the maximum capabilities of high coercive force materialcan only be utilized when certain conditions are present. In therecording process, intense magnetic fields are required, and theseintense fields are obtained by the present invention with a minimumamount of leakage flux which tends to demagnetize the high frequency. Inother words, the effective scanning width of the recording gap isreduced, thus allowing the recording of higher frequencies.

A further feature of the present invention is the ability of headsdesigned in accordance with the teachings of the present invention toerase high coercive force material without overheating of the headstructure. In general, intense magnetic fields in electromagneticapparatus are obtained only by operating the electrical part of theapparatus at high current density. In the head structures of the presentinvention, the copper foil in the gap may be operated at extremely highcurrent density because of its short length and because of rapid heatconduction to relatively heavy masses of copper to which the foil isattached at both ends. In this connection, the present invention isparticularly advantageous in that the high current density is appliedwhere it is needed the most, or, in other words, in the head gap closeto the recording wire.

The head structure of the present invention is also particularlyadvantageous as a play-back head. In conventional play-back heads of theprior art, a compromise has been made in selecting the width of the headgap. As the width of the gap is decreased, the fineness of scanning isimproved, but the leakage flux across the gap surfaces directly underthe record member increases. Since this leakage flux does not thread thecoil, a reduction in output voltage results. This effect is present forall frequencies. At high frequencies, there is an additional effect inprior art head structures. When the head coil is loaded by a resistor,such as is commonly used in the input circuit of a play-back amplifier,or by the distributed capacitance of the coil itself in associatedwiring, the resulting currents in the coil cause an increase in leakageflux. The effect is the same for a head without this additional leakageflux in series with an inductance. In the case of the resistanceloading, the effect is a gradual falling off of the high frequencies.The effect of the capacitance loading is to cause a resonant frequencybeyond which the response of the head is extremely poor or nil. As aresult of these series inductance effects, there is a limit to thenumber of turns that can be placed on a conventional pick-up head and,therelflorei a limit on the voltage which can be supplied bythe With astructure such as that of the present invention, part of the fluxleaking across the gap and all of the flux leaking below the gap linksthe turn in the gap, and therefore, is just as effective in producingvoltage as the flux which follows the path of the core structure. Theresult is an increase in output voltage in medium and low Claims.

2,694,109 Patented Nov. 9, 1954 frequencies, and also at highfrequencies, since the effect of the apparent series inductance of thehead is greatly reduced.

It is an object of the present invention to provide a novel combinedmagnetic transducer head and coupling transformer which is efficient inoperation and rugged and reliable in use.

' A further object of the present invention is to provide a novelelectromagnetic transducer head and assembly which is particularlysuited for use with relatively high coercive force materials such, forexample, as materials having a coercive force in excess of 300 oersteds.

A still further object of the present invention is to provide a novelsingle-turn electromagnetic transducer head.

Still another and further object of the present inven tion is to providea novel electromagnetic transducer head which may be used either as arecording head, a play-back head or an erase head.

The novel features which I believe to be characteristic of my inventionare set forth with particularity in the appended claims. My inventionitself, however, both as to its organization, manner of construction,and method of operation, together with further objects and advantagesthereof, may best be understood by reference to the followingdescription taken in connection with the accompanying drawings, inwhich:

Figure 1 is a front elevational view of an electromagnetic transducerhead embodying the novel teachings and characteristics of the presentinvention;

Figure 2 is a right end view of the electromagnetic transducer headshown in Figure 1;

Figure 3 is a front elevational view of a slotted copper plate employedin the structure shown in Figure 1;

Figure 4 is an end view of the copper plate shown in Figure 3;

Figure 5 is a view of the head lamination employed in the head structureshown in Figure l; and

Figure 6 is a top view of the electromagnetic transducer head shown inFigure l.

This application is a division of my co-pending application for CombinedMagnetic Transducer Head and Coupling Transformer, U. S. Serial No.793,727, filed December 24, 1947, and assigned to the same assignee asthe present invention.

In the particular embodiment of the present invention as illustrated inFigures 1 to 6 of the drawings, the electromagnetic transducer headillustrated includes a head lamination 11 and a transformer core 12,each made of magnetic material having relatively high permeability andrelatively low retentivity. The head lamination 11 as shown in Figure 5of the drawings has an arcuate top edge 13 which is slotted as at 14 toreceive a copper foil or bar 15 which extends at right angles to theplane of the face of the core lamination 11. The top edge 13 is alsogrooved as at 16 to receive a wire or other thread-like magnetic recordmember 17 (shown only in Figure 2). The core 11, of course, acts as alow magnetic reluctance path for the magnetic field about thecurrent-carrying copper bar or foil 15 and tends to concentrate themagnetic field in the small gap 14 across which the wire or othermagnetic record member 17 crosses.

The transformer core 12 may be of any suitable form, but preferably is alaminated simple rectangular shell type core having a center leg 18 uponwhich two pancake coils 19 and 20 are mounted. These pancake coils 19and 20 lie on opposite sides of a copper plate 21 which in theillustrated embodiment of the present invention has the shape asillustrated most clearly in Figures 3 and 4 of the drawings. This plate21 has a central opening 22 which enables the plate to straddle the leg18 of the transformer core 12. The plate 21 also includes two upstandingleg portions 23 and 24 which straddle the head lamination 11 as isclearly shown in Figure 1 of the drawings.

The tops of the legs 23 and 24 are slotted as at 25 to receive thecopper foil or bar 15, the bar 15 being secured to the legs 23 and 24 bysolder or other suitable bonding and electrically conducting material.The copper plate 21 thus, in conjunction with the copper foil or baracts as a single-turn coil for feeding energy to or from the headlamination 11. For example, when the electromagnetic transducer head isbeing used to make a magnetic record on the traveling record member 17,fluctuating electric energy representing the signal to be recorded isfed to the pancake coils 19 and 20, these coils being the primarywindings of the coupling transformer which feeds energy to the headlamination 11. Fluctuating electric current is thus induced in thesingle-turn secondary formed by the copper plate 21 and the copper bar15. The fluctuating electric current is of high current density, thusenabling good recording on high coercive force material used as therecord member 17.

The fluctuating electric current flowing through the bar 15 sets up astrong fluctuating magnetic field around the bar 15. This causeslongitudinal magnetization of the traveling record member 17 as itpasses across the gap 14 in the head lamination 11. On play-back, thereverse operation takes place. This same type of head may also be-usedas an erase head, and very satisfactory resplts are obtained in erasinghigh coercive force mate ria While I have shown a particular embodimentof my invention, it will, of course, be understood that I do not wish tobe limited thereto, since many modifications may be made, and I,therefore, contemplate by the appended claims to cover all suchmodifications as fall within the true spirit and scope of my invention.

I claim as my invention:

1. A combined magnetic transducer head and coupling transformercomprising a transducer core having an edge arranged to have a magneticrecord member pass thereover, said core having a gap therein extendinginwardly from said edge, a transformer core in close proximity to saidtransducer core, a conducting bar extending through said gap and securedto said transducer core, a conducting plate extending around a portionof said transformer core and secured thereto, the ends of said memberbeing electrically connected and secured to opposite ends of said bar,whereby said transducer core is mounted on said transformer core andsupported by said member, and a high impedance winding wound on-saidtransformercore substantially parallel to and in close proximityto saidlow impedance member.

2. A combined magnetic transducer head and coupling transformercomprising a transducer core having an edge arranged to have a magneticrecord member pass thereover, said core having a slot therein extendinginwardly from said edge, a transformer core in close proximity to saidtransducer core, a low impedance closed circuit electrically conductivemember extending around a portion of said transformer core and around aportion of said transducer core and passing through said slot thereof,and a high impedance winding wound on said transformer coresubstantially parallel to said low impedance member and in closeproximity thereto.

3. A combined magnetic transducer head and coupling transformercomprising a transducer core having an arcuate edge arranged to haveamagnetic record member pass thereover, said core having a gap thereinextending inwardly from said arcuate edge, a transformer core in closeproximity to said transducer core, a conducting bar extending throughsaid gap and physically secured to said transducer core, a C-shapeconducting plate extending around a portion of said transformer core andsecured thereto, the ends of said C-shape member being electricallyconnected and physically secured to opposite ends of said bar, wherebysaid transducer core is mounted on said transformer core and supportedsolely by said C-shape member, and a pair of high impedance windingswound on said transformer core on opposite sides of and in closeproximity to said low impedance member.

4. A combined electromagnetic transducer head and transformer comprisinga transformer core, a transducer head core having a pair of closelyspaced poles, said transformer core havinga central leg, a generallyC-shape metal plate extending around said central leg and straddlingsaid transducer head core, a metal bar disposed between said poles insaid transducer head core and extending out on opposite sides thereof,the upper ends of said C-shape metal plate being slotted to receive saidmetal bar, said bar being secured to said ends of said plate and lyingsubstantially in the plane of said plate, and a pair of relatively highimpedance pancake windings also mounted on said central leg on oppositesides of and in close proximity to said metal plate.

5. A. combined magnetic transducer head and coupling transformercomprising a transducer core having an edge arranged to have a magneticrecord member pass thereover, said core having a slot therein extendinginwardly from said edge, 'a transformer core in close proximity to saidtransducer core, a low impedance closed circuit electrically conductivemember extending around a portion of said transformer core and aroundaportion of said transducer core and passing through said slot thereof,and a, pair of high impedance windings wound on said transformer core.on opposite sides of said low impedance member and in close proximitythereto.

References Cited in the filev of thispatent UNITED STATES PATENTS NumberName Date 2,418,542 Camras Apr. 8, 1947 2,423,339 Newman July 1, 19472,532,100 Howell Nov. 28, 195.0 2,539,400 Carnras Jan. 30, 1951 FOREIGNPATENTS Number Country Date 612,450 Germany Apr. 25, 1935

